1. Field of the Invention
The present invention relates to a system for the observation of the traffic in a mobile radiocommunications network such as the GSM (Global System of Mobile Communications).
2. Description of the Prior Art
It will be recalled, for a clearer understanding of the rest of this document, that a network of this kind combines primarily two subsystems as shown in the drawing of FIG. 1:
the B.S.S. radio subsystem (Base Station Subsystem),
the N.S.S. switching and routing subsystem (Network and Switching Subsystem),
The B.S.S. subsystem provides for the distribution of the radiocommunications network. It is constituted by base transceiver stations (B.T.S.) managed by a base station controller (B.S.C.).
A B.T.S. is the element providing the interface between the terrestrial network and the mobile units.
Its task is to provide for exchange on the signalling, speech and data channels between the mobile unit and the G.S.M. network
The location of each B.T.S. is defined by the requirement of radio coverage of a precise zone.
In low-density zones, the base transceiver stations cover a large radius of transmission and reception while in high-density zones, base transceiver stations are more numerous and cover smaller zones.
A B.S.C. manages the base transceiver stations that are attached to it. It carries out radio call procedures, release procedures and also communications holding (power control and handover) procedures.
A B.S.C. carries out a function of concentrating the data links which are PCM (Pulse-Code-Modulated) links by enabling the traffic channels coming from the base stations to be concentrated on a restricted number of channels going towards the mobile services switching center (M.S.C.) to which it is attached.
The B.S.C.s are positioned so as to reduce their number and the distance from the PCM links to be used.
The N.S.S. subsystem is made up of an M.S.C. as well as home location registers (H.L.R.) and visited location registers (V.L.R.).
The M.S.C. ensures the conveyance of communications between fixed and mobile subscribers. It is a digital switch capable of performing all the functions necessary to the management of the calls by the mobile subscribers located in its area.
Moreover, it manages the consequences of the mobility of the subscribers. To do so, it uses the V.L.R.s and H.L.R.s. Each mobile switching center has an associated V.L.R.
The layout of the M.S.C./V.L.R. association is done so as to reduce its distance from the B.S.S. system.
An H.L.R. is a data base capable of carrying out the management of the mobile subscribers. It contains the identity of the mobile unit as well as the data elements which, naturally, are continuously variable. The H.L.R. indicates a V.L.R.
The V.L.R. locally stores the data elements needed for the incoming and outgoing calls of the mobile subscribers recorded in its data base. The mobile subscribers are those that are in the location zones managed by the V.L.R.
The radio interface ensures the communication between the mobile unit and the B.T.S. for the transmission of digital signals. It relies on the LAPDm protocol.
The Abis interface is structured so as to convey the users"" traffic (phone and data) as well as the signalling between the B.S.C. and the B.T.S.
Consequently, it can be subdivided into two distinct parts, one corresponding to the conveyance of the users"" traffic, the other to the conveyance of the signalling related to the setting up of communications and the operation and maintenance of the base station.
The physical access between the B.T.S. and the B.S.C. is obtained by 2048 Kbit/s PCM digital links structured in 32 time intervals of 64 Kbit/s. Each time interval corresponds to a traffic channel used on the radio interface.
The A interface ensures the conveyance of the users"" traffic (phone and data) and the signalling between the B.S.S. and N.S.S subsystems.
The conveyance of the users"" traffic makes it necessary to allocate terrestrial resources between the B.S.S. and the N.S.S. These terrestrial resources are circuits identified by a time interval number and an PCM link number.
The physical access between the B.S.S. and the N.S.S. is obtained by 2048 Kbit/s PCM digital links structured in 32 time intervals.
When a call is being set up, the mobile station makes a first access on the channel of the cell. In response to this, the B.S.C. allocates a first dedicated channel to the station. After the mobile station has taken this radio channel, there is a path between this station and the B.S.C. The mobile station then uses this path to send an initial message.
Upon the reception of the initial message, the B.S.C. sets up a connection with the M.S.C. on the A interface. This connection is dedicated to this mobile station. These two elements, one on the radio interface and the other on the A interface, constitute a dedicated path of the M.S.C.. The dialog can then take place.
According to an earlier system of observation designed to make local observations, the equipment, as shown in FIG. 2, consists of:
a computer supported by an integrated service digital network (ISDN) link used as a remote control, and by a protocol analyzer enabling the traffic of the network to be observed.
However, this system requires the connection, by means of wire-grips, of the four outputs of the analyzer to the four PCM links to be observed. Now, the observation of an PCM link requires the connection of five wires: 2 for transmission, 2 for reception and 1 ground wire.
A physical A interface comprises several PCM links (a number N of links, this number being not always the same one depending on the interfaces). An analyzer AP has a fixed number of PCM channels to be tested. This number is 4. It is therefore necessary first of all to make 4xc3x975=20 manual connections.
A first disadvantage of this system is that a connection sometimes generates disturbances on the corresponding M.I.C links leading to communications cuts.
A second disadvantage of this system is that it requires a manual connection that has to be made at the site itself. In practice, 20 connections are required for four PCM links to be tested.
Moreover, this making of the manual connection dictates a trip to the M.S.C. which is generally located tens of kilometers away from the place of observation, i.e. from the place in which the equipment for controlling the observation of the traffic is located.
The present invention makes it possible to overcome these problems and, for this purpose, proposes the connection, between the analyzer and the PCM links, of an automatic switching interface to route an output of the analyzer towards any of the PCM links to be observed.
Moreover the interface can be remote controlled by means of an ISDN link connecting a control unit to the protocol analyzer. Through this link, the protocol analyzer is, so to speak, transferred to the location of the command. The control parameters are transmitted by the analyzer to the switchbox. The switchbox ensures switching between its various outputs and the PCM channels that are to be observed, depending on the instructions that it receives from the analyzer.
The present invention is aimed more particularly at a system for the observation of the traffic of a mobile radiocommunications network comprising, per site, a mobile services switching center connected to base station controllers by N digital transmission links (PCM links) and/or a base station controller connected to base transceiver stations by N digital transmission links (PCM links); at least one protocol analyzer comprising n outputs, wherein chiefly the system furthermore comprises means for switching over to n inputs and N outputs, capable of routing the signals of each input to one of the outputs, the n inputs corresponding to the n outputs of the analyzer and the N outputs being connected to the N PCM links to be observed.
According to another characteristic the system comprises a unit for the driving of the protocol analyzer connected to the analyzer by a digital transmission line to achieve the remote control of the running of the analysis of the network and the driving of the switching means.
Advantageously, the line is an integrated services digital network (ISDN) line.
According to another characteristic, the switching means comprise a switching assembly formed by flip-flop circuits and relays and a control unit capable of actuating the switching relays.
According to another characteristic, the switching means can be put into operation or deactivated without any interruption of the telephone calls.
Another object of this invention relates to a switching device for a traffic observation system comprising at least one protocol analyzer (AP) with n outputs, designed to analyze N digital transmission links (PCM links), said device comprising, for this purpose, at least n inputs liable to be connected to the n outputs of an analyzer and at least N outputs liable to be connected to N digital transmission links (PCM), and being capable of routing each input to one of the outputs.
According to another characteristic, the switching device comprises a switching assembly comprising one set of flip-flop circuits per output of the analyzer of the relays so that a relay is placed at each output of each flip-flop circuit and a control unit capable of actuating the switching relays.
The switching device can be connected to the traffic observation system without interruption of the telephone calls.
According to another characteristic, the switching device takes the form of a box that is independent and can be connected to the outputs of the analyzer and to the PCM links to be observed.